• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Autopilot for Roberston Stol 185

F

frstnflt

Registered User
Is there a viable new generation autopilot for a 1975 A185F with Roberston Stol? I know just fly the airplane but mine is a family IFR hauler and I need to be able to study an approach plate in the clouds or turn around and yell at my kids.
Trutrak and GFC 500 both say not compatible with RSTOL.
Trio seems to have a bad rep by installers but it looks cool and seems to do what I need. Navigation will be exclusively be a Garmin 375.
STEC sent a generic message suggesting the 55X. $19K+ for just the hardware? No thanks.

IMG_1508.jpg
 

Attachments

  • IMG_1508.jpg
    IMG_1508.jpg
    97.4 KB · Views: 347
stewartb said:
Why in incompatibility? APs are pretty simple. Move controls one way or the other.
Click to expand...

I'd ask the same thing. Must be for roll control, the RSTOL pulleys, etc create a slightly different install, and they've never gone through the approval??

How about a two axis autopilot?

MTV
 
Not sure why, but almost all autopilots I've worked with have restrictions on models of aircraft or even avionics units installed.

Web
 
email from Garmin:
The Robertson STOL kit droops the leading and trailing edge devices which could change the behavior of the AP considerably. Garmin has no approved data for this installation with a Robertson STOL Kit. The Robertson also changes the original roll bellcrank which makes our installation physically impossible.

The below excerpt is from our Master Drawing List documentation which clearly prohibits this, no questions.


1


From Trutrak website:

[h=2]PLEASE NOTE CESSNA 180 AND 185 MODELS EQUIPPED WITH A ROBERTSON STOL KIT ARE NOT COMPATIBLE WITH OUR CURRENT INSTALLATION.[/h]
 
frstnflt said:
email from Garmin:
The Robertson STOL kit droops the leading and trailing edge devices which could change the behavior of the AP considerably. Garmin has no approved data for this installation with a Robertson STOL Kit. The Robertson also changes the original roll bellcrank which makes our installation physically impossible.

The below excerpt is from our Master Drawing List documentation which clearly prohibits this, no questions.


1


From Trutrak website:

PLEASE NOTE CESSNA 180 AND 185 MODELS EQUIPPED WITH A ROBERTSON STOL KIT ARE NOT COMPATIBLE WITH OUR CURRENT INSTALLATION.
Click to expand...

Thats what I figured. Minor detail, though: on late model planes the RSTOL doesn’t droop the leading edge. And in fact, the system does nothing to the trailing edge unless you deploy flaps. Who uses the autopilot on one of these things with flaps deployed?

But, the last point is the issue: The roll bellcrank interferes with their servo. And they’re not interested in redesigning and certifying it to work.

And I understand that. So why don’t they just say up front: Our unit doesn’t fit on this mod.....

MTV
 
The roll servo is in the wing? Move it. It pulls on a cable. Where it pulls on it isn't critical. More FAA certification BS, no doubt.
 
Have you looked at the Century autopilots? https://www.centuryflight.com/stcs/stc-list/cessna-aircraft/1304-skywagon.html They are approved with the Robertson. I have had a Century IIB in my 185 working flawlessly for 40+ years.

I also used an Stec pitch control system PSS for a while since the Century 3 was not approved. It was horrible so I threw it out. It uses ambient air pressure changes and an accelerometer to control pitch. Poor idea. It only worked in absolutely still air.
 
I just picked up a 182R for a guy that has the RSTOL and a KAP 150. It was simply placarded "Autopilot must be off for all operations with flaps extended."
 
185 autopilot

frstnflt said:
not familiar with century. Any idea on the cost?
Click to expand...
a long time ago I put an STEC 55 in my A185E. This plane has a Bush STOL kit installed. When I asked for approval from STEC, they gave it to me with a minor flight restriction.
 
There has been a lot of discussion on this topic in multiple places. Maybe I can shed some light on the subject.

Autopilots are designed, developed and certified in aircraft based on the type design of the aircraft. Keep in mind it's the engineering that is certified, not the aircraft. What makes your aircraft "airworthy" is the fact that it conforms to the type design and is maintained in an airworthy state.

When someone comes along and makes a modification to an airplane, that airplane no longer conforms to the original type design, but that individual (or entity) can test their modifications against the regulations and obtain a "supplemental type certificate (STC)", which allows for the change in type design.

When the mentioned autopilot(s) were certified in the Cessna 180/185, the engineering data specified that servos are installed in very specific locations, bridle cables are attached to specific bell cranks with specific tensions, and certain settings were configured within the autopilot to ensure the autopilot performs its intended function and performs to certain specifications.

Modern day, digital autopilots are very complex systems (think computer logic, not necessarily mechanical installation) that use a feedback loop that is processed at 50 hertz or more to make very small (and fast) adjustments via servos in order to control an airplane with a very high amount of precision. Most autopilots use what are called "gains" in order make adjustments to that feedback loop to achieve the desired level of performance. These gains are what turn a slow, lethargic response into a "corners likes she's on rails" performing autopilot that allows you to fly coupled approaches to 200 ft within a needle width and hold an altitude within less than +/- 5 ft. In other words, modern day, digital autopilots should fly the airplane better than you do in most cases. And you should expect that type of performance.

That performance, and the level of safety that the FAA demands (and you should also expect) is contingent upon that autopilot being installed according to the engineering data that was used to certify it, and also contingent upon your airplane meeting its type design.

The performance and safety of the autopilot depend very much on where the servo is installed, and where upon you pull on a bell crank and with how much force based on the gearing ratios of the system. Alter a bell crank, relocate a servo, or alter the bridle cable tension from the engineering drawings, and your installation no longer complies with type design.

The FAA takes compliance with type design very seriously, and no more serious of an issue than with flight controls. Think about this: would you rather have an engine failure or a flight control failure? An engine failure still affords you the ability to decide where you're going to crash. A flight control failure...

I understand the frustration, particularly with the FAA and the autopilot manufacturers and with regard to some topics, I share your frustration. But flight controls are a serious matter that should not be taken lightly.

Your best tactic to affect change is to let your preferred autopilot manufacturer know that you have an airplane model that they create a product for, but does not accommodate your specific aircraft type design because you have a certain STC applied to your airplane. If there is a large enough pool of airplanes like yours, basic economics will solve the problem for you.

Hope that helps.
 
I installed an S tec in my Robertson STOL 400 Comanche. No issues. Worked perfectly. I had to retention flight cables to bring the aircraft controls into spec to keep it from wondering but that was the only issue, and that was the first and only correction. It was a full Robertson with all the features. Flew very stable and control forces were nothing noteworthy. Not sure what the issue is? . RSTOL is primarily for landing and taking off short. I never used the autopilot on short final dragging it in with the power up or on a take off.
 
Last edited:
This is a new post on a 3 year old thread, but I am in need of photos or drawing showing how the Robertson or STEC bracket attaches to the Robertson STOL bellcrank, allowing for autopilot use in a 185.

I’ll include a photo of the adapter bracket, but I do not have a drawing or instructions for install, and before I yank the entire Aileron bellcrank out I thought I’d ask.
Image1691521748.956966.jpg

The drawing underneath is for a std non-Robertson bellcrank.


Transmitted from my FlightPhone on fingers… [emoji849]
 

Attachments

  • Image1691521748.956966.jpg
    Image1691521748.956966.jpg
    61.1 KB · Views: 56
I've got an A185F w/ RSTOL and the Stec 55X there isn't a bracket like that picture on my plane.

Andy

Farmboy said:
This is a new post on a 3 year old thread, but I am in need of photos or drawing showing how the Robertson or STEC bracket attaches to the Robertson STOL bellcrank, allowing for autopilot use in a 185.

I’ll include a photo of the adapter bracket, but I do not have a drawing or instructions for install, and before I yank the entire Aileron bellcrank out I thought I’d ask.
View attachment 66622

The drawing underneath is for a std non-Robertson bellcrank.


Transmitted from my FlightPhone on fingers… [emoji849]
Click to expand...
 
andy schwartz said:
I've got an A185F w/ RSTOL and the Stec 55X there isn't a bracket like that picture on my plane.

Andy
Click to expand...

You might be surprised Andy, if you were to look close at the aileron bellcrank.

Nonetheless I was able to acquire a drawing, thanks for the help.

Peter


Transmitted from my FlightPhone on fingers… [emoji849]
 
any chance you can share the installation insturcitons from RSTOL? I purchased mine with it already installed and didn't get the installation instructions.

thanks
Andy
 
Andy, I don't have anything regarding Robertson kit. I was looking for the bracket install info.
 
I have an F model 206 with full Robertson kit and sportsman cuff. Installed an s-tec 30 A/P with altitude hold over 20 years and 3000 hrs ago and havn’t had an issue. I realize 206 wing is different but I’d do it again in a heartbeat.
 
There is a lot of discussion concerning various autopilot installation in C-180/185 Robertson STOL kit aircraft. I have only seen discussion, no one has stepped up to the plate with a solution.

I am an A&P with IA, I have years of experience in general aviation repair and maintenance, especially with Cessna aircraft.

I decided to find if there was a work-around for my Robertson STOL C-185. I purchased the Aero Cruise 100. If I could not find a work around, I had a stock C-180 to install it in.

I have successfully installed the Aero Cruise 100 (TruTrak) autopilot in my 1975 C-185F with Robertson kit installed. Installation IAW STC with a minor alteration. This was a simple, straight forward solution to the interference with the Robertson Aileron droop cam mechanism. Reposition push-pull tube from rear to fdw bell crank attach point.

(Minor Alterations means an alteration having no appreciable effect on the weight, balance, structural strength, powerplant operations, flight characteristics or other characteristics affecting the airworthiness of any aircraft.)


Flight tested and signed off. Executed FAA Form 337 and logbook entry with minor alteration to STC. Autopilot works great.
 
You can install a Garmin GFC500 and sign it off using Garmin’s NTO letter.
We did one this past summer.


Sent from my iPhone using SuperCub.Org
 
You must log in or register to reply here.
Back
Top